The overall objective of this research is to better understand the host defense mechanisms responsible for prevention and recovery from respiratory disease. Three model systems will be used: I. Immunity to influenza in the ferret, II. Immunity to influenza in the mouse, and III. Post influenzal bacterial infection in the mouse. The principal objective relative to influenza immunity is to understand the role of the four components of the immune system, a) serum-antibody, b) secretory-antibody, c) systemic cell-mediated immunity, and d) local cell mediated immunity in protecting man and other animals against influenza infection so as to be better able to stimulate immunity in man and thereby decrease the morbidity and mortality due to influenza. Fundamentally, we have two approaches to demonstrating the role of each of the four components: 1) transfer of immunity from an immune to a nonimmune ferret via one or a combination of the components, or 2) ablation of existing immunity by the selective destruction or inhibition of one or a combination of the four components. The principal objective relative to post influenzal bacterial infection is to study adherence of bacteria to the virus infected mouse trachea and the role of this adherence in the production of bacterial pneumonia.